Three gun color tube with central gun of smaller cross-section than lateral guns



July 16. 1968 H. DE FRANCE ETAL 3,393,336 THREE GUN COLOR TUBE WITH CENTRAL GUN 0F SMALLER CROSS SECTION THAN LATERAL GUNS Filed May 17. 1966 2 Sheets-Sheet l 8 N9- 1 We +Ve Fig: I

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A alfil de FRAMc F m CAI-6L KM 1 K t l 19 Ju y 16 68 H. DE FRANCE ET AL 3,393,336 THREE GUN COLOR TUBE WITH CENTRAL GUN 0F SMALLER CROSS SECTION THAN LATERAL GUNS Filed May 17. 1966 2 Sheets-Sheet 2 Q n C) LL. 3 C) n O o G L.-

C\! G 0 G L I/uvMTDRSZ (e/um 3e FEAMc 0908 CA-H M 64 A-GHUT United States Patent 1 Claim. (in. 313 /0 ABSTRACT OF THE DISCLOSURE A three-gun color television tube in which the electron beam of a central gun of smaller cross section is directed on the screen elements which phosphoresce in a blue color whereas the beams of the lateral guns, whose cross sections are greater, are directed to the red and green screen elements, whereby the spacing of the beams may be reduced.

The present invention relates to tricolour television receiver tubes, comprising a screen with red, green and blue phosphor elements and three guns, namely the red gun, the green gun and the blue gun, for reproducing the optical red, green and blue components of the picture through the impact of their respective beams on the phosphor elements of the corresponding colours.

According to the invention, there is provided a television cathode ray tube having a screen with phosphor elements of three colours, one of which is blue, and three guns respectively associated with the phosphor elements of each colour, wherein the diameter of the gun associated with the blue phosphor elements is markedly smaller than the diameter of the other two guns.

For a better understanding of the invention and to show how the same may be carried into eflect reference will be made to the drawing accompanying the following description and in which:

FIGURE 1 shows a tricolour tube of known construction;

FIGURE 2 is a vertical section of the gun arrangement of the tube of FIGURE 1; and

FIGURES 3, 4 and 5 show in vertical section the arrangement of the guns according to the present invention.

The tube of FIGURE 1 is a tube with vertical phosphor strips, with focusing grid and three guns, wherein the grid and the screen are flat and rectangular.

Screen 2 comprises regularly repeated red, blue and green strips, R, B, and G, wherein three adjacent strips of different colours form a triplet.

The drawing shows only a few phosphor strips whose dimensions have been exaggerated to make the drawing clearer. In fact, the tube comprises a large number of triplets, each of which corresponds to one picture point on each line of the picture.

In front of the screen 2 is a grid 3 of fine wires arranged parallel to the strips, the number of wires corresponding to the number of triplets. Also, the distance between the grid 3 and the screen 2 has been exaggerated in the drawing.

Three guns 4, 5 and 6 of equal axial length with electrostatic focusing, with their axes in the same horizontal plane, supply three beams.

Between the output of the guns and near the grid, the tube envelope 1 has a conductive coating 9, forming the second anode of the tube.

Between the anode 9 and the grid 3 is another peripheral electrode 8, the socalled correction electrode, which is assumed in the drawing to be formed from a metal frame but which may also be formed by a conductive coating on the wall of the envelope, insulated from the coating 9. v

The tube also comprises a conventional electromagnetic deflector 7, identical to that of monochrome tubes and shown only partly in the drawing. Such a tube operates as follows:

The screen 2 is brought to a potential Ve which is high relative to that of the cathodes of the guns and the grid 3 is brought to a lower positive potential Vg; the grid-screen assembly forms a system of convergent cylindrical lenses for the electron beams coming from the guns. The conductive coating 9 on the inner wall of the tube has a potential equal to the highest potential of the guns and the grid potential Vg is substantially equal thereto.

The beams coming from the guns 4, 5 and 6, referred to respectively as the red gun, the blue gun and the green gun, are modulated by the red, blue and green signals. Under the combined effect of the horizontal and vertical deflections, caused by the deflecting system 7, the three beams are deflected from their straight paths and sweep the screen line by line, perpendicularly to the grid wires and to the phosphor strips.

This simultaneous sweeping is effected at any moment in such a way that the three beams respectively issued from the red, blue and green guns, after converging at a point P substantially in the plane of the grid, impinge respectively on the red, blue and green strips of the same triplet.

This result is obtained by a complex arrangement using: a slight inclination (of the order of 1 degree and not shown in the drawing) of the axes of the two lateral guns against the centre axis; the focusing action of the grid-screen assembly; a so-called dynamic convergence system, not shown in the drawing, which impresses on at least two of the three beams, at the outputs of their respective guns, slight auxiliary deflections varying with the general sweeping motion; and the correcting action produced by the electrode 8, which is brought to a voltage which varies as a function of the general sweeping motion, this electrode serving essentially to provide a precorrection of the parasitic deflection associated with the focusing of the beams in the grid-screen space.

This tube is known in the art and, as described, so far, presents no special novel feature except that generally the blue gun is not the centre gun and that the blue strip is generally not the centre strip of the triplets defined by the grid wires. It is shown only by way of non-limitative example of tricolor tubes to which the invention is applicable.

The advantages, especially for obtaining the convergence, of the use of three coplanar guns in a tube of this type are well known, but in fact such a gun structure cannot be used with very narrow phosphor strips, for example, 0.25 mm. wide, the use of such narrow strips being, on the other hand, of advantage for the horizontal definition of the picture.

In fact, for a given length of the neck of the tube, the axes of the three guns must be the nearer to each other, the narrower are the strips while, for reasons of compactness, it is not desirable to enlarge the tube.

On the other hand, the spot of a beam will be the finer, which is desirable for the horizontal and vertical definition of the picture, the greater is the diameter of the three guns, and from this point of View it is undesirable to go below 8 or 9 mm. For this reason, a gun arrangement is generally adopted in which the centre gun is placed slightly higher than the two other guns which makes the electronic optics of the tube more complicated.

The present invention is based on the following fact:

Statistically speaking, the brightness of the picture and thereforeits 'definiti on is supplied esentially by the red and-thegreemoptical-components of the picture andthe--- reproduction of the blue components is practically without effect on the brightness "except in large areas with blue colour such as. the sky or the sea, where very good definition is not important. i

As a consequence, a fairly large spot is acceptable for the beam issuing. from the blue gun and this can have a smaller-aperture, -,for example 4 to 5 mm-.; if in addition, care is taken toarrange.the'blu e gunas the centre gun, the triplets defined on the screen by the grid wires being naturally such that the blue strip is the centre strip, the axes of the three guns can be substantially aligned as shown in FIGS. 2 and 3, which show the section in a vertical plane near that end of the guns which faces the grid, of a conventional three gun arrangement with 9 mm. diameter gun and of an arrangement according to the invention with two lateral 9 mm. diameter guns and one central 5 mm. diameter gun. In these drawings and in the following ones the scales has been doubled for the sake of clarity. The sections of the axes of the guns are marked by a cross.

It must be understood that the invention is not limited to a tube of the type hereinbefore described or to a tube with a screen with vertical strips or more generally to a tube with a screen with strips. It may also be used with a screen with oblique phosphor strips horizontally swept by the three beams, with a screen with horizontal phosphor strips or with a screen with phosphor dots.

The invention also applies to three guns with axes in the same vertical plane or in a plane in any direction.

On the other hand, the invention may be used not only with three guns with coplanar axes but also with guns in which the axes of the two lateral guns are in the same, for example, horizontal plane and the centre gun with a smaller diameter has an axis which is not in this plane.

The invention makes it possible to bring the axes of these three'guns nearer "to'each other-so'that the difierence in height of the third can be reduced. FIGS. 4 and 5 show cross-sections of arrangements for guns of this type.

Of course the invention is not limited to the embodiments described and shownlwhich were given solelyby wayofexample; 1

What is claimed is:'

1. A color television picture tube having an axis and including a screen having red, green and blue phosphorescent element s arranged in strips approximately 0.25 millimeter wide, a central electron gun and two lateral guns closely adjacent to said central gun, said guns having substantially the same axial length and each gun being adapted to emit an electron'beam, means for deflecting said beams so as. to scan said screen, said deflecting means including means for directing said beams respectively to said red, blue and green elements only, said central gun havingan axis substantially coinciding with the axis of said tube, said lateral guns'having respective axes spaced from said coinciding axesin opposite directions and in a commonplane' therewith, said lateral guns each having a diameter of at least eight millimeters,

v said central gun having across-section substantially smaller than the cross-section of each of said lateral guns, and said deflecting means'including-means for directing the beam of said central gun to saidblue elementsonly.

- References Cited ROBERT SEGAL, PrimaryExaminer. 

